Siril workflow: preprocessing

I would like to record how I process my photos on here, mostly because there isn’t a whole lot of good documentation on Siril, and also because I will probably forget between imaging sessions.

The first step to getting your light frames ready is also produce good calibration frames.

  1. Take dark frames at the same ISO and shutter speed as you did your lights. Put a dark cover over the end of the telescope. I take about 20 of these.
  2. Take bias frames at the same ISO but at the quickest shutter speed your camera has. Again, I take about 20 of these.
  3. Take flat frames at the same ISO and an appropriate shutter speed such that the histogram is not clipping. I use a white cloth cover of the end of the telescope with a flood flashlight to produce an even white field of light. Still, about 20 images is good.

Organize these frames in a common directory for your target, with the calibration frames in directories called “biases,” “flats,” and “darks,” respectively.

I use the following script to process all of these files into usable masters. You can place the script in a file in ~/.siril/scripts to get the scripts to register and appear when Siril is opened. Name the file whatever you want the script to appear as in Siril.

#build master-bias
cd biases
convertraw bias_
stack bias_ med -nonorm
cd ..

cd flats
#preprocess flats
convertraw flat_
preprocess flat_ -bias=../biases/bias_stacked

#build master-flat
stack pp_flat_ med -norm=mul
cd ..

#build master-dark
cd darks
convertraw dark_
stack dark_ med -nonorm
cd ..

Next, load up Siril and set the working directory as the base of your images. Your script should appear in the Scripts menu at the top of the screen. This will start chugging along and turning all of the calibration frames into usable masters. After this is complete, you can import your light frames the normal way, with no debayering. This will create your sequence of lights. Now, go to the Preprocessing tab.

These are the settings I like to use. I am no expert and don’t know the details on what any of these things really do, but my recent testing seemed to give me the best results with these settings. You will just want to use the master dark and flat frames that the script created. You don’t need the bias, as it is already included in the flat frame.

Click “Start Preprocessing” and it will create a new sequence of images with the master frames applied. You can then move on to registration.